1. Field of the Invention
The present invention relates to an apparatus and a method for upgrading or remediating semiconductor devices. In particular, the present invention relates to utilizing a remediation, modification or upgrade chip or other component in a piggyback configuration with an existing bare chip assembly to achieve an upgrade, modify chip operating parameters or remedy a design or fabrication problem.
2. State of the Art
Definitions: The following terms and acronyms will be used throughout the application and are defined as follows:
BGAxe2x80x94Ball Grid Array: An array of minute solder balls disposed on an attachment surface of a semiconductor die wherein the solder balls are refluxed for simultaneous attachment and electrical communication of the semiconductor die to a printed circuit board.
COBxe2x80x94Chip On Board: The techniques used to attach semiconductor dice to a printed circuit board or similar carrier substrate, including flip chip attachment, wirebonding, and tape automated bonding (xe2x80x9cTABxe2x80x9d). COB also references the resulting end product.
Flip Chip: A chip or die that has a pattern or array of terminations spaced around the active surface of the die for face down mounting of the die to a substrate.
Flip Chip Attachment: A method of attaching a semiconductor die to a substrate in which the die is inverted so that the connecting conductor pads on the face of the device are set on mirror-image pads on the substrate (such as a printed circuit board) and generally bonded by solder reflux or a conductive polymer curing.
Glob Top: A glob of encapsulant material (usually epoxy or silicone or a combination thereof) surrounding a semiconductor die in a COB assembly.
PGAxe2x80x94Pin Grid Array: An array of small pins extending substantially perpendicularly from the major plane of a semiconductor die, wherein the pins conform to a specific arrangement on a printed circuit board or other substrate for attachment thereto.
SLICCxe2x80x94Slightly Larger than Integrated Circuit Carrier: An array of minute solder balls disposed on an attachment surface of a semiconductor die similar to a BGA, but having a smaller solder ball pitch and diameter than a BGA.
TABxe2x80x94Tape Automated Bonding: A conductor placement structure wherein conductive traces preformed on a dielectric film or flexible sheet, such as a polyimide, are used to electrically connect bond pads of a semiconductor die to conductors of a carrier such as a leadframe or printed circuit board.
State-of-the-art COB technology generally consists of three semiconductor die-to-printed circuit board conductive attachment techniques: flip chip attachment, wirebonding, and TAB.
Flip chip COB attachment consists of attaching a semiconductor die, generally having a BGA, a SLICC or PGA, to a printed circuit board. With the BGA or SLICC, the solder or other conductive ball arrangement on the semiconductor die must be a mirror-image of the connecting bond pads on the printed circuit board such that precise connection is made. The semiconductor die is bonded to the printed circuit board by refluxing the solder balls. With the PGA, the pin arrangement of the semiconductor die must be a mirror-image of the pin recesses on the printed circuit board. After insertion, the semiconductor die is generally bonded by soldering the pins into place. In all of the foregoing techniques, insulative underfill encapsulant is generally disposed between the semiconductor die and the printed circuit board for environmental protection and to enhance the attachment of the die to the board.
Wirebonding and TAB attachment to produce a COB generally begin with attaching a semiconductor die to the surface of a printed circuit board with an appropriate adhesive, such as an epoxy. In wirebonding, a plurality of bond wires is extended and attached, one at a time, between each bond pad on the semiconductor die and a corresponding lead or trace end on the printed circuit board. The bond wires are generally attached through one of three industry-standard wirebonding techniques: ultrasonic bondingxe2x80x94using a combination of pressure and ultrasonic vibration bursts to form a metallurgical cold weld; thermocompression bondingxe2x80x94using a combination of pressure and elevated temperature to form a weld; and thermosonic bondingxe2x80x94using a combination of pressure, elevated temperature, and ultrasonic vibration bursts. With TAB, ends of metal traces carried on an insulating tape or film such as a polyimide are respectively gang-bonded using thermocompression techniques to the bond pads on the semiconductor die and to the lead or trace ends on the printed circuit board. An encapsulant is generally subsequently applied over the die and attendant the bond wires to prevent contamination or any physical damage to the assembly.
During a production run of an integrated circuit, a design parameter may change or a design or fabrication error may be detected in one or more circuits of a semiconductor chip. When such occur, the semiconductor chips of that production run may have to be scrapped if not exhibiting at least minimum performance characteristics. Although it may be possible to remediate the semiconductor chips with the addition of an adjacent chip or other circuit on the board, increased miniaturization of components and the boards to which they are mounted, as well as greater packaging density of integrated circuit assemblies, reduces or eliminates the potential space or xe2x80x9creal estatexe2x80x9d on the board upon which to locate remediation or upgrade circuitry or chips. Further, in many instances, it would be desirable to employ semiconductor dice in circuits for which they were not initially designed or intended, such as employing a die having a lower voltage requirement in a circuit providing a higher voltage power input. Such adaptability of dice to various operating environments may be significant, and even critical, during cycles in the industry wherein certain components are in short supply and others might be substituted if a viable technique for doing so existed.
U.S. Pat. No. 5,012,323 issued Apr. 30,.1991, to Farnworth teaches combining a pair of dice mounted on opposing sides of a leadframe. An upper, smaller die is back-bonded to the upper surface of the leads of the leadframe via a first adhesively coated, insulated film layer. A lower, larger die is face-bonded to the lower leadframe die bonding region via a second, adhesively coated, insulative, film layer. The wirebonding pads on both the upper die and lower die are interconnected with the ends of their associated lead extensions with gold or aluminum bond wires. The lower die must be slightly larger than the upper die in order that the die pads are accessible from above through a bonding window in the leadframe such that gold wire connections can be made to the lead extensions.
U.S. Pat. No. 5,128,831 issued Jul. 7, 1992, to Fox et al. teaches vertically stacked die, each in a sub-module, the sub-modules connected by solder-filled vias and the assembly connected to a board through a PGA.
U.S. Pat. No. 5,291,061 issued Mar. 1, 1994, to Ball teaches a multiple stacked die device containing up to four stacked die supported on a dice attach paddle of a leadframe, the assembly not exceeding the height of then-current single die packages, and wherein the bond pads of each die are wirebonded to lead fingers. The low profile of the device is achieved by close-tolerance stacking which is made possible by a low-loop-profile wirebonding operation and thin, adhesive layers between the stacked dice.
U.S. Pat. No. 5,323,060 issued Jun. 21, 1994, to Fogal et al. teaches a multichip module that contains stacked die devices, the terminals or bond pads of which are wirebonded to a substrate or to adjacent die devices.
U.S. Pat. No. 5,422,435 to Takiar et al. teaches dice stacked to form a multi-chip module (CM) and having wire bonds extending to each other and to the leads of a conductor-bearing carrier member such as a -leadframe.
U.S. Pat. No. 5,434,745 issued Jul. 18, 1995, to Shokrgozar et al. teaches a structure similar to that of Fox et al. with stacked sub-modules electrically connected at their peripheries by a conductive epoxy.
U.S. Pat. No. 5,438,224 issued Aug. 1, 1995, to Papageorge et al. teaches a multi-die assembly employing face-to-face dice connected to an interposed TAB tape or flex circuit, which in turn is connected to an underlying board.
U.S. Pat. No. 5,455,445 issued Oct. 3, 1995, to Kurtz et al. teaches an MCM of vertically stacked dice employing vias extending through the semiconductor material of the die substrates for vertical electrical interconnection.
All of the above mentioned patents relate to increasing conductor-bearing integrated circuit density. However, none of these patents deal with remediating, modifying or upgrading semiconductors and semiconductor assemblies.
Therefore, it would be advantageous to develop a technique and assembly for remediating, adapting, modifying or upgrading semiconductor die assemblies using remediation, adaptation, modification or upgrade chips in combination with commercially available, widely practiced semiconductor device fabrication techniques.
The present invention relates to an apparatus and a method for upgrading, adapting, modifying or remediating semiconductor devices utilizing a remediation or upgrade chip in a piggyback configuration with an existing bare chip assembly to achieve an upgrade, adapt to an assembly, modify an operating parameter or remedy a design or fabrication problem.
As mentioned above, during a production run of an integrated circuit, a design parameter may change, a design or fabrication error may be detected in a semiconductor chip or the like. When such problems are encountered, the semiconductor chips of that production run might normally be scrapped. Although it may be possible to remediate such a semiconductor chip with the addition of a circuit to the board on which the chip resides, increased miniaturization of boards and cards and greater packaging density of integrated circuits eliminates the potential space or xe2x80x9creal estatexe2x80x9d upon which to locate remediation or upgrade circuitry or chips.
Further, it may be desirable to upgrade an unflawed but obsolete chip design while a new design is being developed and introduced so as to maintain market share and serve customer needs.
In addition, the viability of adapting chips to operating environments, such as power sources for which a particular chip is not designed, is extremely desirable, especially during periodic component shortages. One specific example would be use of a regulator to enable a 3.3 V pail to access a 5 V system. Another example of an operating environment adaptation would be the addition of an output driver to strengthen a chip""s signal output to a circuit which would not respond to the chip""s original signal.
The present invention solves the real estate problem by mounting the remediation chip on a face surface of the original chip (the term xe2x80x9cremediationxe2x80x9d or xe2x80x9cremediatingxe2x80x9d will be used for purposes of this application to mean either remediating the original die to fix an error, adapting the original die to meet at least one changed design or operating parameter, upgrading the original die with additional circuitry, or the like).
The basic assembly of the present invention comprises an original or primary die with a patch or remediation die adhered thereto. The patch die is attached to the primary die by a layer of adhesive. The adhesive is preferably an electrically insulative adhesive, as required or desired, to electrically isolate the primary die from the patch die. Depending on the adhesive, the assembly might be xe2x80x9ccuredxe2x80x9d to affix the dice together. It is, of course, understood that other types of adhesives, such as a pressure sensitive adhesive or a tape segment carrying the same, could be used to hold the dice together.
Generally, both the primary die and patch die have a plurality of bond pads. The dice are attached such that the bond pads of each face in a common direction. A substrate with leads or a plurality of lead fingers from a leadframe extend toward the primary die (the term xe2x80x9csubstratexe2x80x9d will be used for purposes of this application to mean either a substrate carrying traces or other conductors or a leadframe). The substrate conductors may make electrical contact with the bond pads on the patch die or primary die. Generally, the electrical contact is made with a plurality of bond wires. However, the electrical contact could be made with TAB connections, lead fingers in a leads-over-hip (LOC) or even a leads-between-chip (LBC) connection configuration or the like. A second electrical connection is made between the patch die and the primary die. The second electrical connection can likewise be made with bond wires or TAB connections. However, the second electrical connection can also comprise a lower bond pad (actually a via) disposed on the adhesion surface or back side of the patch die. A flip chip electrical connect, such as solder or a conductive polymer, achieves an electrical connection between the lower patch die bond pad or via end, and the primary die bond pad.
The patch die may receive an output signal from the primary die, or receive an input signal from or provide an output signal to the substrate trace or leadframe. The circuitry in the patch die remediates, modifies, adapts or performs upgrade functions and outputs the corrected or modified signal to the primary die or a substrate conductor or lead finger (depending on the input).
A glob top or dammed encapsulant may be applied over the entire assembly to protect same from contamination and physical damage. After application of the glob top or other encapsulant, the primary die, for all intents and purposes, is indistinguishable, both physically and in performance, from a die designed from the outset to exhibit the modified and desired characteristics of the assembly.
Another embodiment comprises a patch die which may span the width and/or length of the primary die. In this embodiment, the patch die has a plurality of first bond pads on a patch die face surface, preferably in the approximate position of the primary die bond pads. The patch die further includes a plurality of lower bond pads (via ends) on a patch die back side. A flip chip type electrical connect, such as solder, a conductive polymer or a conductor-loaded polymer, achieves an electrical connection between the lower bond pads and the primary die bond pads. The substrate conductors or lead fingers extend toward the primary die and are connected to their respective bond pads on a face surface of the patch die with a plurality of bond wires. The remediation, adaptation, modification or upgrade is achieved with the patch die. As previously discussed, the patch die either receives an output signal from the original die or an input signal from the substrate or lead finger. The circuitry in the patch die remediates, adapts, modifies or performs upgrade functions and outputs the corrected signal to the original die or the substrate lead or lead finger (depending on the input).
Yet another embodiment of the present invention comprises the use of multiple interacting patch dice either separately attached to the original die or stacked atop one another. Multiple patch die assemblies are necessary when a single chip cannot by itself provide all of the circuitry required for remediation or where the amount of real estate on a primary die will not allow for a single large patch die.
In the multiple stacked assembly, a lower patch die is attached to the original die with a first layer of adhesive. A back surface of an upper patch die is attached to a face surface of the lower patch die with a second layer of adhesive. A plurality of bond wires makes electrical contact between the substrate leads or lead fingers and a plurality of bond pads on an upper patch die face surface of at least one of the patch dice. A plurality of upper-to-lower patch die bond wires makes electrical contact between a plurality of bond pads on the upper patch die face surface and a plurality of respective die bond pads on the lower patch die face surface. A plurality of stack-to-primary die bond wires makes electrical contact between a plurality of bond pads of at least one of the patch dice and a plurality of primary die bond pads.
In the separately attached multiple die assembly, multiple patch dice are each attached directly atop the original die. The patch dice electrically interact with one another, as well as the primary die, and in connection with the substrate or leadframe in the manner discussed above to achieve remediation of the original die.
While the specification concludes with claims particularly pointing out and distinctly claiming that which is regarded as the present invention, the advantages of this invention can be more readily ascertained from the following description of the invention when read in conjunction with the accompanying drawings in which:
FIG. 1 is a top plan view of a prior art wire bond/leadframe semiconductor assembly;
FIG. 2 is a top plan view of a prior art leads over chip semiconductor assembly;
FIG. 3 is a top plan view of a preferred assembly of the present invention;
FIG. 4 is a side cross-sectional view of the assembly of FIG. 3 along line 4xe2x80x944;
FIG. 5 is a side cross-sectional view of an alternate assembly;
FIG. 6 is a side cross-sectional view of another alternate assembly;
FIG. 7 is a top plan view of another preferred assembly of the present invention;
FIG. 8 is a side cross-sectional view of the assembly of FIG. 7 along line 8xe2x80x948;
FIG. 9 is a side plan view of yet another alternate assembly of the present invention;
FIG. 10 is a side plan view of a multiple patch die assembly of the present invention;
FIG. 11 is a side plan view of an alternative multiple patch die assembly of the present invention; and
FIG. 12 is a top plan view of yet another alternative multiple patch die assembly of the present invention.